The steam generators equipping nuclear power stations have several thousand inverted U-tubes arranged in the form of groups or bundles and whose two ends traverse a thick plate, called a tube plate, in which each of the tubes is welded and then expanded. This tube plate ensures the heat exchange between the water, known as the primary water, flowing in the primary circuit of the reactor and water flowing in the secondary circuit, known as the secondary water. The temperature of the primary water within each of the tubes consequently decreases significantly between their intake end and their outlet end. For this reason, the term "hot branch" and "cold branch" is commonly used for the upward and downward branches of the tubes, respectively extending the intake and outlet ends for the primary water.
The inverted U-shaped tubes of the tube bundle of a steam generator are housed within a vertically axial, cylindrical envelope, in which the tube plate is fixed. As a result most of the tubes have geometrical characteristics which differ from one another. In view of the fact that the location of manufacture of the tubes is generally different from that of the steam generator assembly, the individual identification of the tubes must take place before they are moved to the assembly point. At present, this identification takes place by placing on each of the tubes an adhesive label, on which is written a code guaranteeing its installation at the appropriate location on the steam generator tube plate. As soon as this location has been identified, the label is removed and the tube is put into place in the steam generator and welded to the tube plate.
This procedure for the identification of the tubes is only partly satisfactory. Thus, the adhesive labels can be lost during tube handling operations and they require a not insignificant, subsequent control time, with all the associated error risks. Moreover, the present individual tube identification procedure in no case makes it possible to identify the tubes in cartesian coordinates on the tube plate, in order to carry out on the tubes machining, checking or maintenance operations, after they have been fixed to the tube plate.
In particular, it is not at present possible to individually identify the tubes of a generator in cartesian coordinates, in order to carry out automatically machining in the factory or sealing on site of certain of these tubes, following an inspection carried out using an eddy current probe. There is consequently an appreciable time loss, and on the actual site the inspection personnel is exposed to the highly irradiating medium of the primary circuit for a much longer time than is strictly necessary for sealing certain of the tubes.
Moreover, the individual identification of the tubes from the start of their manufacture would make it possible to control the latter under particularly advantageous conditions, which is not possible when the tubes are identified with the aid of labels which can only be placed on the tubes when their manufacture is completed.